This invention relates to a multilayered, uniaxially oriented shrink film. More specifically, the invention relates to halogen-free multilayered shrink films useful in labeling articles.
Shrink film has been used for years to encapsulate articles. The shrink film must be able to shrink sufficiently to provide a smooth consistent package. Previously, shrink films have been polyolefins and polyolefin blends, polyethylene terephthalate glycol (PETG), vinyl and styrene films that were and are used extensively in the food and packaging industry to protect and preserve articles, such as food. Shrink films are also used to label containers. Initially, labeling operations were carried out using processes and methods that required the formation of a tube or sleeve of the heat shrink film which was then placed over the container and heated in order to shrink the film to conform to the size and shape of the container.
More recent packaging processes do not require a preformed sleeve and permit the application of the film directly from a continuous roll of film material onto the container. High speed continuous operations generally employ biaxially oriented polypropylene shrink films. Such polypropylene shrink films have the ability to shrink up to about 25% in the machine direction as tested per ASTM Method D 1204. However, it is often desirable to obtain a shrinkage greater than 25%. New containers being introduced into the market have ergonomic features, with contours that have high shrink demand. Such containers require labels that shrink to greater than 25%.
Polyvinyl chloride (PVC) films provide acceptable shrinkages of about 40%. However, such PVC shrink films do not have sufficient heat stability. After formation of the shrink film, the film should not shrink prematurely. Often the film is exposed to relatively high temperatures after formation, such as in transport. It is desired that the shrink film not shrink until application with heat to the bottle or article. Another disadvantage of PVC shrink films is the potential environmental impact of PVC film. Concern over the adverse affect of halogens on the ozone layer has lead to efforts to provide halogen free shrink films.
As an additional consideration, high speed continuous operations require the use of an adhesive that will form an adequate bond between the container and the label. More specifically, the bond must be such that it will not separate at the seam during the heat shrinking step. The bond should also form a smooth package which will not bubble or cause creasing of the film during application. As the level of shrinkage desired is increased, the adhesive used in the high speed applications must be able to provide an adequate bond while maintaining an acceptable appearance, e.g., without distortion. The adhesive must be compatible with the particular shrink film material used.
It is desirable to have a film that provides high shrinkage, e.g. shrinkage of 25% and higher. It is also desirable to have the films be halogen free. Additionally, it is desirable to have labels that can be applied using a continuous roll process and that can be applied at high speeds.
U.S. Pat. No. 4,194,039, issued to Mueller, relates to a multi-layered polyolefin shrink film. The film has three layers comprising a core layer of a blend of ethylene-vinyl acetate copolymer with ethylene-butylene copolymer and each skin layer of ethylene-propylene copolymer.
U.S. Pat. No. 4,196,240, issued to Lustig et al, relates to heat shrinkable multilayer packaging film of blended copolymers and elastomers. The multilayer film includes a first outer layer comprising a blend of propylene-ethylene copolymer having a high isotactic molecular structure with less than about 6% by weight being ethylene and having a melt flow of from about 1.5 to about 18 decigrams per minute; and (butene-1)-ethylene copolymer having a high isotactic molecular structure with less than about 10% by weight ethylene and having a melt flow of about 0.1 to about 5.0 decigrams per minute, and a thermoplastic elastomer selected from the group consisting of ethylene-propylene copolymers and ethylene-propylene diene terpolymers, the ratio of the weight of the propylene-ethylene copolymer to the (butene-1)-ethylene copolymer being from 2:1 to about 1:2 and the thermoplastic elastomer being present from about 10% to about 50% by weight. The multilayer film also has an outer layer comprising an ethylene-(butene-1) copolymer having a melt flow of from about 0.1 to about 1 decigram per minute, having a density of from about 0.916 to about 0.920 gram per cubic centimeter, and being a linear polymer. The multilayer film is also biaxially oriented.
U.S. Pat. No. 4,207,363, issued to Lustig et al, relates to flexible heat-shrinkable multilayer film for packaging primal meat. The multilayer film includes (1) a first outer layer comprising a blend of a propylene-ethylene copolymer, a (butene-1)-ethylene copolymer and a thermoplastic elastomer selected from the group consisting of ethylene-propylene copolymers and ethylene-propylene diene terpolymers; (2) a first core layer connected to the first outer layer and being capable of being stretched during the biaxial orientation of the multilayer film and comprising an extrudable adhesive; (3) a second core layer connected to the first core layer and serving as an oxygen barrier to prevent the meat cut from spoilage and being compatible to the biaxial orientation and heat shrinking of the film; and (4) a second outer layer comprising an ethylene vinyl acetate copolymer. The multilayer film is biaxially oriented.
U.S. Pat. No. 5,190,609, issued to Lin et al, relates to stable pressure sensitive shrink label technique. The heat shrink labels are formed from a polyolefin, such as a polypropylene, and have a permanent acrylic pressure sensitive adhesive on one side thereof and may be mounted on a release coated backing strip. A metallized layer and open style graphics may be applied to the labels. The graphics may be protected by varnish or a second layer of heat shrinkable polyolefin material.
U.S. Pat. No. 5,443,895, issued to Peiffer et al, relates to multilayer transparent polyolefin film for application in shrink labeling. The heat shrinkable film comprises a base layer prepared from a polypropylene-containing polymer and a hydrocarbon resin. The base layer contains about 5 to 40% by weight of a polypropylene homopolymer, 0 to about 30% by weight of a hydrogenated hydrocarbon resin having a softening point in the range from about 80 to 125xc2x0 C. and from about 30 to 95% by weight of a random ethylene-propylene copolymer.
U.S. Pat. No. 5,494,717, issued to Peiffer et al, relates to matte, biaxially oriented, multilayer polypropylene film of high shrinkage, and processes of making the same. The multilayer polypropylene film comprises at least one base layer containing a propylene polymer and a propylene polymer mixture in at least one outer layer that comprises a mixture or a blend. The mixture contains copolymers and terpolymers of alpha olefins containing 2 to about 10 carbon atoms and high density polyethylene.
U.S. Pat. No. 5,691,043, issued to Keller et al, relates to uniaxially shrinkable biaxially oriented polypropylene film and it method of preparation. The polypropylene film comprises a polypropylene-containing core layer comprising at least 70% by weight of said multilayer film and at least one polyolefin-containing skin layer adjacent to the core layer. The core layer is prepared by biaxially orienting a coextrudate and thereafter orienting said coextrudate by stretching 10 to 40% in the machine direction. The core layer contains isotactic polypropylene and a modifier which reduces the crystallinity of the polypropylene by increasing chain imperfections or reducing isotacticity of the polypropylene containing core. The modifiers include atactic polypropylene, syndiotactic polypropylene, ethylene-propylene copolymer, propylene-butylene copolymer, ethylene-propylene-butylene terpolymer and linear low density polyethylene. The skin layers are selected from the group consisting of polypropylene, ethylene-propylene copolymer, polyethylene and ethylene-propylene-butylene terpolymer.
The present invention relates to a halogen-free, uniaxially oriented multilayered heat shrink film comprising (A) a core layer comprising a blend of (i) a copolymer of propylene with an alpha olefin and (ii) a homopolymer of propylene or butylene, or a copolymer of butylene with an alpha olefin, the core having an upper and lower surface; (B) a first skin layer on the upper surface of the core layer; and (C) a second skin layer on the lower surface of the core layer, wherein each skin layer independently comprises a copolymer of ethylene or butylene with an alpha olefin and wherein the ultimate shrinkage of the film is at least about 40% at 270xc2x0 F. (132xc2x0 C.).
In another embodiment, each of the skin layers, B and C, of the uniaxially oriented multilayered heat shrink film comprises a a blend of (i) a homopolymer of propylene or a hompolymer of butylene or a copolymer of butylene with an alpha olefin and (ii) a copolymer of propylene with an alpha olefin.
The invention further relates to a halogen-free, uniaxially oriented multilayered heat shrink label comprising (A) a core layer comprising a blend of (i) a copolymer of propylene with an alpha olefin and (ii) a homopolymer of propylene or butylene, or a copolymer of butylene with an alpha olefin, the core having an upper and lower surface; (B) a first skin layer on the upper surface of the core layer; and (C) a second skin layer on the lower surface of the core layer, wherein each skin layer independently comprises a blend of (i) a homopolymer of propylene or a homopolymer of butylene or a copolymer of butylene with an alpha olefin and (ii) a copolymer of propylene with an alpha olefin; and (D) an coated on at least a portion of at least one of the skin layers, wherein the ultimate shrinkage of the label is at least about 40% at 270xc2x0 F. (132xc2x0 C.).
The invention further relates to articles, including articles such as bottles and containers. The films have good shrinkage and heat stability, and the labels produced from the films may be applied at high speeds using a continuous roll process.
The invention further relates to a process for making a uniaxially oriented heat shrink label having an instantaneous shrinkage of at least 30% at 275xc2x0 F. (135xc2x0 C.).